Because the resonant cavity of a laser is much larger than the wavelength of the optical signals supported therein, it is inherently capable of resonating at a plurality of wavelengths whose nominal center-to-center spacings are inversely proportional to the length of the cavity. How many of these longitudinal cavity modes are supported depends upon the gain curve of the active laser material. In particular, oscillations occur for only those modes whose gain exceeds a threshold level fixed by the overall cavity losses. If more than one mode can be supported, there is a tendency for the laser to switch back and forth among these modes, giving rise to what is known as mode partition noise. As pointed out by K. Ogawa in a paper entitled "Analysis of Mode Partition Noise in Laser Transmission System," published in the May 1982 issue of the IEEE Journal of Quantum Electronics, mode partitioning among the longitudinal modes of a laser diode, combined and the chromatic dispersion of an optical fiber medium, is a limiting factor for single-mode optical fiber systems employing direct modulation of laser diodes. It is, accordingly, important to establish and maintain stable, single-mode operation of the laser.